Method of forming a thin multichip module

ABSTRACT

An improved multichip semiconductor module compatible with existing SIMM memory sockets comprising a molded module frame and a composite semiconductor substrate subassembly received in a cavity in said frame. The composite semiconductor substrate subassembly or subassembly(s) comprises a plurality of semiconductor devices which are connected to electrical contacts on an edge of the molded frame by a variety of configurations described herein. In one embodiment of the invention, the subassembly(s) includes a composite substrate which comprises a thin metal cover plate and thin laminate circuit which is bonded to the metal cover plate by a film adhesive. The composite substrate provides a mounting surface for the placement of semiconductor devices and their associated passive components. In some of the embodiments disclosed herein, the subassembly(s), comprising a cover plate with the composite substrate attached thereto, is permanently attached to the molded frame by a rectangular ring formed from an anisotropic, electrically conductive adhesive material. In other embodiments, the subassembly(s) are removably attached to a module frame socket. The composite substrate employed in the present invention offers the advantages of allowing the components to be pre-assembled, tested and repaired prior to final attachment into the molded frame, and aids in the transfer of heat away from the semiconductor devices operating thereon. The module frame provides a protective enclosure for the multichip semiconductor devices and can be molded for compatible mating with existing SIMM sockets. Other high density contact means provide a greater interconnect capability.

RELATED APPLICATION DATA

This is a divisional of application Ser. No. 08/472,532, filed Jun. 7,1995 entitled "Thin Multichip Module" and issuing on May 12, 1998 asU.S. Pat. No. 5,751,553, which is a divisional of application Ser. No.08/138,829 filed Oct. 18, 1993, now U.S. Pat. No. 5,731,633 issued Mar.24, 1998 entitled "Thin Multichip Module", which is acontinuation-in-part of application Ser. No. 07/947,293, filed on Sep.16, 1992, now abandoned, entitled "A Thin MultiChip Module."

FIELD OF THE INVENTION

The present invention relates generally to means for encapsulatingmicroelectronic devices. More specifically, the present inventionprovides an improved module which significantly increases the packagingdensity of microelectronic components.

BACKGROUND

The electronics industry has a continuing goal of increasing componentpackaging density in an effort to obtain increased functionality andconsequent performance in smaller volumetric size. The principalroadblocks in meeting this goal have been the lack of industry standardsfor form factors and a flexible design which can be adapted to differingdevice types. Another significant impediment to increased packagingdensity has been the lack of an efficient means for dissipation ofthermal energy generated by the devices.

One of the largest microelectronic device module markets is that relatedto dynamic random access memories (DRAM's). Since its introduction in1983, the Single In-Line Memory Module or SIMM, disclosed generally inU.S. Pat. No's. 4,656,605 and 4,727,513, has grown to become thepreferred module configuration for the DRAM semiconductor market. Amongthe advantages offered by the SIMM are the following: (1) itssignificant packaging density increase achieved over prior chip mountingconfigurations, (2) the convenience for modular replacement or upgrade,and (3) availability of multiple, low-cost manufacturing sources.

A continuing industry trend towards increasing performance and smallersize, however, foreshadows the need for an even more compact module thanthe present SIMM is able to provide. The quest for ever faster dataprocessing and more compact, lightweight, thin, portable, hand-heldelectronic products necessitates newer semiconductor packaging schemesthat enable aggregate assemblages of bare silicon devices to beinterconnected together and mechanically protected inside a thin,lightweight module. Because of the handling difficulty and expenseassociated with repairing or replacing bare silicon chip devices, thereis an anticipated need for an adaptable multichip module which providesa means for increasing packaging density while maintaining minimumexpense. This present invention, described in greater detail below,seeks to satisfy this need within the electronic industry.

Though semiconductor memory devices occupy the vast majority of themodule market today, there is also a growing requirement to modularizeother semiconductor components including, but not limited to,microprocessor, application specific integrated circuits,telecommunication and other device types. Accordingly, the presentinvention provides an upgrade path for a greater number of interconnectpins/pads and improves the thermal dissipation characteristics overpresent day microelectronic device modules.

SUMMARY OF THE INVENTION

The present invention comprises various embodiments of an improvedsemiconductor module that houses a considerably larger number ofsemiconductor devices in a given volume. The module preferably isadapted for insertion into a mating socket and is removable forreplacement, repair, configuration changes, or recycling. The preferredembodiments of the semiconductor module of the present invention arealso backward compatible with existing SIMM sockets. Other embodimentsare compatible with other standards, such as the PCMCIA (PersonalComputer Memory Card International Association).

In one embodiment of the present invention, the module is broadlycomprised of a molded module frame and a composite semiconductorsubstrate subassembly (abbreviated: "subassembly" or "subassembly(s)" or"subassemblies") received in a cavity in the frame. The compositesemiconductor substrate subassembly, or subassembly, comprises aplurality of semiconductor devices which are connected to electricalcontacts on an edge of the molded module frame by a variety ofconfigurations described herein.

In one embodiment of the invention, the subassembly includes a compositesubstrate which comprises a thin metal cover plate and thin laminatecircuit which is bonded to the metal cover plate by a film adhesive. Thecomposite substrate provides a mounting surface for the placement ofsemiconductor devices and their associated passive components. In someof the embodiments disclosed herein, the subassembly is permanentlyattached to the molded module frame by a rectangular ring formed from ananisotropic, electrically conductive adhesive material. In otherembodiments, thin laminate circuits are applied to either side of acover plate, and semiconductor devices are applied to the laminatecircuits. A protective overcoat can be applied over the semiconductordevices, as desired. Other embodiments include folded or U-shapedlaminate circuits with semiconductor devices and heat dissipating coverplates applied to respective surfaces, as desired. The variousembodiments of the subassembly employed in the present invention alsoprovides for a more efficient means for conducting thermal energy fromthe semiconductor devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of the major components of a first embodimentof the thin multichip module of the present invention;

FIG. 1A illustrates the volumetric savings of the semiconductor moduleof the present invention as compared to standard SOJ-type SIMM modules;

FIG. 2 is a cross-sectional view taken along lines A-A' of FIG. 1showing details relating to electrical contacts of the molded moduleframe and composite semiconductor substrate subassembly of the presentinvention;

FIG. 3 is a similar view to that in FIG. 2 with exception that a thinrectangular battery is substituted for the thin metal cover plate;

FIG. 4 is an exploded view of the major components of an alternateembodiment of the thin multichip module of the present invention;

FIG. 5 is a perspective view of the electrical contacts of the moldedmodule frame of the embodiments shown in FIGS. 1-4;

FIGS. 6A-6D illustrate an alternate embodiment of individual contactelements employed in the multichip module of the present invention;

FIGS. 7A-7C illustrate another alternate embodiment of individualcontact elements employed in the multichip module of the presentinvention;

FIGS. 8A-8C illustrate yet another alternate embodiment of individualcontact elements employed in the multichip module of the presentinvention;

FIGS. 9A-9B show alternate embodiments of edge mount clips forelectrical contacts on the molded module frame of the present invention;

FIGS. 10A-10B illustrate optional thermal dissipation features builtinto the thin laminate circuit of the composite substrate of the presentinvention;

FIG. 11 illustrates optional thermal dissipation features formed on theoutside surface of the composite substrate of the present invention;

FIG. 12 illustrates an implementation of stacked memory chips for use onthe composite substrate assembly of the present invention;

FIG. 12A illustrates an embodiment using standard silicon plates in lieuof the substrate subassembly;

FIG. 13 is a exploded view of the major components of an alternateembodiment of the thin multichip module of the present inventioncomprising multiple composite semiconductor substrate subassemblies(hereinafter referred to as "subassemblies");

FIGS. 14, 14A and 14B are cross-sectional views of FIG. 13 detailingalternate embodiments of the molded module frame intended for assemblywith multiple composite subassemblies;

FIG. 15 and 15A are full cross-sectional views of an embodiment for themolded module frame detailed in FIG. 6, illustrated with thesubassemblies in a final assembled configuration. FIG. 15 details across-section view emphasizing the molded portions of the molded moduleframe which are positioned between the contacts;

FIG. 15A is similar to FIG. 15, but emphasizes the metal contact portionof the molded module frame and illustrates an additional interconnectionat the stepped ledge or edge of the molded module frame opposite thecontact. This enables a crossover electrical path between the thinlaminate circuits across the stepped ledge or edge;

FIG. 16 is similar to FIG. 15A, and illustrates how a crossoverelectrical path between the thin laminate circuits can be establishedusing a folded section of flexible thin laminate circuit;

FIGS. 17A-17B illustrate an alternate embodiment of the presentinvention comprising an overcoated composite semiconductor substratesubassembly (hereinafter referred to as an overcoated subassembly);

FIGS. 18A-18D illustrate alternate embodiments of overcoatedsubassemblies in which semiconductor devices and components arepositioned on both sides of a metal plate or thin plate-like battery andelectrically joined along the edge by a single flexible circuit foldedover and around the edge;

FIG. 19 illustrates an example of how the overcoated subassemblies ofFIGS. 17-18 may be mated to a module frame socket premounted on acircuit board;

FIG. 20 is an exploded view of an alternate embodiment of FIG. 16 inwhich crossover of the electrical paths between opposing subassembliesis provided by a separate piece of flexible laminate circuit joinedalong the edge;

FIG. 21 is a cross-sectional view of FIG. 20, after the separate pieceshave been joined, showing the spatial relationship of the opposingsubassemblies folded towards each other;

FIG. 22 is a cross-sectional view of yet another embodiment of FIG. 21in which the volumetric void between adjacent subassemblies has beenfilled with a semi-rigid compound. [The resultant rigid assembly isshown superimposed above a cross-sectional view of a module frame socketsimilar to that shown in FIGS. 19, 29 or 30];

FIG. 23 is a cross-sectional view of an alternate embodiment of FIG. 22.

FIG. 24 is a cross-sectional view of yet another alternate embodiment ofFIG. 22.

FIGS. 25-25B illustrate the spatial relationship of opposingsubassemblies joined by a single flexible circuit prior to being foldedtowards each other;

FIG. 26 is a cross-sectional view of an embodiment of FIG. 25B in whichmultiple rows of contacts are provided by a single flexible circuitfolded over and around the edges of opposing subassemblies. [Theresultant assembly is shown superimposed above a cross-sectional view ofa module frame socket that is wrapped with a corresponding flexiblelaminate circuit];

FIG. 27 details in cross-sectional view the embodiment of FIG. 26 inwhich contacts along the edges of opposite and opposing subassembliesare mated to a module frame socket exhibiting multiple independentcontacts;

FIG. 28 details in cross-sectional view the embodiment of FIG. 26 inwhich contacts along the edges of opposing subassemblies are mated to amodule frame socket exhibiting independent and bifurcated or redundantcontacts;

FIG. 28A is a cross-sectional view of a module that has semiconductordevices mounted on all four surfaces of the subassemblies;

FIGS. 29-29A illustrates a perspective and cross-sectional view of amodule similar to that shown in FIG. 23 being mated to a module framesocket exhibiting independent, surface-mount contacts; and

FIG. 29B is a cross-sectional view of a module similar to the moduleshown in FIG. 29A connected to a socket employing a conductiveelastomeric contact;

FIG. 30 illustrates a perspective view of the module in FIG. 21 beingmated to a module frame socket exhibiting contacts similar to FIG. 6;

FIG. 31 is a flowchart diagram illustrating a method for assembling thethin multichip module according to various embodiments of the presentinvention;

FIG. 32 illustrates a composite substrate panel; and

FIG. 33 illustrates a composite substrate panel like that shown in FIG.32 including slots separating the composite substrate.

It is to be understood that the various drawings described herein arenot shown to scale, unless specifically stated otherwise.

DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS

The various embodiments of the multichip module 10 of the presentinvention can be understood by referring initially to FIG. 1, which isan exploded view of the major components of an embodiment of the moduleemploying a molded module frame 12 and subassembly 32. As shown in FIG.1A, this new invention enables a substantial reduction in the volumetriccapacity and areal spacing between multiple adjacent vertical rows orhorizontal layers of modules. Thus, a much greater number or volume ofsemiconductor devices can be included in a given space than thatpreviously known in the art.

The module shown in FIG. 1 comprises a molded module frame 12(hereinafter referred to as either "molded frame" or "module frame" or"frame") having electrical contacts 22, composite substrate 46 includingcover plate 48, laminate circuit 50 and film adhesive 52, and aplurality of semiconductor device 54 mounted to the composite substrate46. An anisotropic ring 58 is optionally used to connect the compositesubstrate 46 to the molded frame 12. The module 10 is preferably adaptedfor mating to a module socket. Other embodiments of the module of thepresent invention do not include a molded frame or module frame as partof the module, but are adapted for insertion into a module frame socketwhich essentially acts as the molded module frame for the module.

Molded Module Frame

In the embodiment of FIG. 1, the molded module frame 12 comprises aninternal cavity 14 which extends over a substantial portion of thelength and width of the module to provide a nesting area for electroniccomponents in the finished module assembly. The molded module frame 12can be manufactured from an injection molded, thermoplastic materialsuch as a liquid crystal polymer (LCP) or "Ryton™." Both of thesematerials allow consistent and repeatable control over the dimensions ofthe molded frame 12. However, it should be obvious to one versed in theart that several other materials can be substituted without departingfrom the scope or spirit of this invention. For example, molded frame 12can also be constructed from single or multiple laminate layers of epoxyglass materials--similar in composition to conventional printed circuitboard (PCB) products--which have been shaped by stamping, pressing ormachining processes to produce features similar in function to thosedescribed above. Alternatively, molded frame 12 can be formed from oneof several ceramic based materials processed though a firing kiln orhydraulic press by techniques well known within the industry orcomprised of silicon nitride or carbon-graphite material, as desired.Alternatively molded frame 12 can also be formed from an opticallytransparent glass or plastic to facilitate transmission of light signalsbetween the module socket and the semiconductor devices.

The molded module frame 12 comprises first and second major parallelplanes, illustrated by reference numerals 16 and 18, respectively, thatare separated by a specified edge thickness, illustrated by referencenumeral 20. An array of contact pads 22 along one edge of frame 12provides electrical connection between the semiconductor devicescontained within the interior of the module and an appropriate matingsocket or circuit board. In the embodiment illustrated in FIG. 1, frame12 is provided with two optional end holes 24 and a comer notch 26.These features are used for proper mating of the module to presentlyavailable SIMM sockets supplied by several connector manufacturers. Inanother embodiment, the module 12 is adapted to conform to the PCMCIAstandard. Other embodiments, such as illustrated in FIGS. 7-9, 19, 29,and 30, can exclude these specific molded features, or can include otherappendages, slots, clips or posts as described hereinbelow to assist inthe final mounting of subassembly(s) 32 to the molded frame 12 or themolded frame to the main circuit board.

The internal cavity 14 can extend either partially or completely throughthe stepped ledge 30 and/or edge thickness 20, depending upon thespacing requirements of the components contained in the module. Variousembodiments of molded floor 28 are illustrated in cross-section FIGS. 2,3, 14-14B, 15, 15A, and 16. In cross-section FIGS. 2 and 3, which aretaken along section lines A-A' of FIG. 1, the floor 28 is shown moldedflush to the second major plane 18 forming a single internal cavity openon plane 16. Although it is possible to construct the frame to have asingle internal cavity, it is also possible to create first and secondinternal cavities by forming a thin, integrally molded floor 28positioned along the centerline of the module thickness. In theembodiments illustrated in FIGS. 14-14B, 15, 15A, and 16, for example,molded floor 28 is shown along the centerline of the module thickness toform first and second internal cavities open on planes 16 and 18respectively. In these embodiments, the first and second internalcavities are on opposite sides of the frame 12, as shown.

Referring again to the molded frame 12 of FIG. 1, a stepped ledge 30 isformed along the circumference of the cavity(s) 14 to provide areceiving area for mating subassembly(s) 32 described in greater detailbelow. In the preferred embodiment, the ledge 30 is recessed below thefirst major plane 16 such that after subassembly(s) 32 is positioned andsealed or fixed in place, the outer surface of subassembly 32 and majorplane 16 of molded frame 12 are substantially flush to one another. Inthe embodiment shown in FIG. 14 having two internal cavities, the ledges30 in each cavity are recessed below the first major plane 16 in thefirst cavity and the second major plane 18 in the second cavity. In someembodiments (FIG. 14B), multiple ledges can be employed. Alternatively,the ledges can be simple extensions of major plane 16 and/or major plane18, as illustrated in FIG. 14A, placing subassembly(s) 32 further awayfrom the center line of the module thickness, thus allowing more spacingfor internal components. In this embodiment, subassemblies 32 project ashort distance above major plane 16 and/or major plane 18 and aresurrounded by a molded appendage or rib 31. Alternatively, inembodiments substituting a module frame socket (12E-H) in place of amolded frame 12 the ledges 30 can be substantially recessed below majorplane 16 and/or major plane 18, as illustrated in FIGS. 22 and 26-28,such that these planes are situated above subassemblies 32. In theexamples shown in FIGS. 22 and 26-28, molded appendages 31 alsopartially enclose the edges of subassemblies 32.

Contacts

Referring again to FIG. 1, the array of contact pads 22 on the edge ofthe molded frame 12 are electrically connected to the interior steppedledge 30 of the molded frame. As shown in FIGS. 2, 3 and 5, arrayedalong the interior stepped ledge 30 are a multiplicity of terminationpads 34, each electrically paired with an associated external contactpad 22. It should be noted that contacts in the preferred embodiment arearrayed along the edge(s) of greatest length, as shown in FIG. 1.However, in an alternate embodiment, the contacts can be arrayed alongthe edge(s) of the shorter length, in lieu of or in addition to contactsarrayed along the edge(s) of the longer length. In one embodiment of theinvention, each of the contact pads 22 and termination pads 34 areformed by a selective plating process that deposits a conductive metalpattern extending from the edge of the molded frame 12, across thesurface of the frame, and down a vertical wall or inclined plane 36, asshown in FIGS. 2, 3, and 5 and across the surface of the ledge 30. Inembodiments having two internal cavities on opposite sides of the frame12, similarly positioned pairs of contact pads 22 and termination pads34 on opposite planes of the molded frame 12 can be electricallyconnected by an electrically conductive shunt 21 across the lower edgeof the frame 12, as illustrated in FIGS. 2, 3, 5, and 14-14B, or leftelectrically isolated.

Plating techniques that can be commonly employed to produce themulti-leveled paths of electrical conduction on the molded frameinclude, but are not restricted to, electrolytic or electroless platedcopper, nickel, gold, or tin/lead alloys. These and other pure metalsand alloys can be selectively plated or deposited onto selected portionsof the molded frame 12 via surface treatment and masking techniquesknown and available within the molded PCB industry. Alternatively,various plating and/or molding processes can be employed separately orcombined with metal filled inks or powders to produce electricallyconductive pads and traces on the molded frame through methods wellknown within the industry.

As the need arises for increasing numbers of control functions, signalsand data in/out connections, the plating process can be adjusted toreduce the contact pad-width 23 and contact-to-contact pad-pitch 25, asshown in FIG. 5, or higher contact density can be obtained by integrallyincorporating into frame 12 an array of stamped or etched metalcontacts, as shown in FIGS. 6A-6C, or by inserting stamped or etchedmetal contacts into receptacles pre-molded in the edge of the frame 12,as shown in FIG. 6D. The array of stamped or etched metal contactscomprises a plurality of thin, closely spaced plates that areelectrically insulated from one another by encompassing mold material orother insulator. The contacts can be incorporated into frame 12 as aseparate pre-molded array, and molded simultaneously with frame 12, orapplied after the frame is molded. These metal contacts have exposededges extending from the bottom edge of the molded frame 12 across thecontact pad surface plane and across the interior stepped ledge of theframe. The edges of the stamped or etched contacts can be recessedbelow, be substantially flush, or project above the surrounding moldedsurfaces.

The above-described electrical contact arrangement may be understood byreferring to FIGS. 6A-6C. FIG. 6A is an illustration of an array 36 ofindividual contact members 38. The edges of the individual contacts 38provide electrical interconnections across the interior ledge 30 andexterior surface of the frame 12 corresponding to the contact pads 22and termination pads 34 discussed above. For example, once the array 36of contacts 38 have been molded or inserted into the edge of the frame12, as illustrated in FIGS. 6A and 6C, the edges 22' and 34' of theindividual contacts 38 correspond to the respective contact pads 22 andtermination pads 34 discussed above in connection with the priorembodiments. FIG. 6C is a cross-sectional illustration of the contactspositioned inside frame 12. This figure also illustrates an additionalelectrical contact surface resulting from the projection of an endportion 22" of a contact 38 from the edge of the frame 12, correspondingto element 21 of FIGS. 2, 3, and 5.

Additional embodiments based on the concept of integrally molded orinsertable contact members are shown in FIGS. 7A-C, 8A-C, 19, 22, 27,28, 29-29B, and 30. When contact members are formed by a stamping oretching process, simple appendages can be included to customize thecontacts for a "through hole" leaded contact 37 or a "surface mount"leaded contact 39. Examples of these are illustrated in FIGS. 7A-C and8A-C. Adjusting the centerline of the "through hole" lead 37' enablesthe distance, D, between the adjacent contacts 37 to be adjusted (D')for standard or non-standard hole patterns on the main circuit board asillustrated in FIGS. 7B and 7C, when adjacent contacts in the array arealternately rotated 180 degrees with respect to each other. By moldingor inserting "surface mount" leaded contacts 39 in alternatingorientations as illustrated in FIGS. 8B and 8C, solder pads on the maincircuit board are optimally spaced on alternating sides of the module,and a more stable mounting base is provided with contacts 39'.Additional support is provided at both ends of the molded frame 12, aslater described in connection with FIG. 9B, by inserting or molding aformed metal clip or post 41 into the bottom-end of molded frame 12.

Use of flat surfaced contact pads 22 located at the bottom edge of themolded frame 12, as shown in FIG. 1, is the preferred configuration forthis invention for backward compatibility with present SIMM sockets.However, an alternative embodiment of the invention includes formedmetal clips over the edge of the molded frame to produce a "leaded"version of the invention for direct solder mounting of the module to aPCB using either "through-hole" or "surface mount" soldering technology.FIG. 9A is an illustration of the molded frame 12 having a plurality ofleads 40 attached to the contact pads 22 for use in a "through hole"soldering application. FIG. 9B is an illustration of plurality of leads40' attached to the contact pads 22 for use in a "surface mount"soldering application. In this embodiment of the invention, an end post42 integrally molded at both extreme ends on the molded frame 12 isincluded to assist in maintaining proper retention and alignment of themodule in the main circuit board during the "surface mount" solderingprocess. These end posts 42 would typically be molded with differingcross-sectional diameters, i.e., one larger than the other, to mate withappropriately sized holes within the main circuit board, therebyenabling the modules to be correctly oriented and secured againstmovement during the soldering process.

In yet another embodiment, intended principally for frames 12 fashionedfrom a ceramic material, stamped metal leads are braze soldered orwelded to metallized contact pads along the edges, resembling inappearance those shown in FIG. 9.

Yet another embodiment, designed principally for subassembly(s) 32containing semiconductor or other devices which employ lightemitting/receiving elements for chip-to-chip communication and datatransfer, as discussed elsewhere, the frame 12 can include or substitutelight channeling structures or elements such as fiber optic strands orbundles in place of conventional metal contacts. Alternately, frame 12can be molded of an optically transparent material, fashioned to conductlight signals from the edges to interior devices, as previouslymentioned.

In yet another embodiment (FIG. 29B), a `z-axis` elastomeric electricalconductor can be integrally molded with molded frame 12, or inserted ascontact members of an array.

Composite Semiconductor Substrate Subassembly

Details relating to the composite semiconductor substrate subassembly(abbreviated: "subassembly") 32 will now be discussed by referring againto FIG. 1. The subassembly includes a composite substrate 46 whichcomprises a thin metal cover plate 48 and thin laminate circuit 50 whichis bonded to the metal cover plate 48 by a film adhesive 52. Thecomposite substrate 46 provides a rigid mounting surface for theplacement of semiconductor devices 54 and their associated passivecomponents 56. The subassembly 32 is preferably attached to the moldedframe by a rectangular ring 58 formed from an anisotropic, electricallyconductive adhesive material. In its final form, the subassembly 32total thickness, including semiconductor devices and passive components,would generally range from 0.010-0.040 inches in order to fit within thepresent 0.050-inch standard SIMM substrate thickness specification.However, in other applications, the individual subassembly and moldedframe thicknesses may be appropriately increased or decreased to adjustfor varying types of mounted devices, components, and structures on themodule 10.

Cover Plate

The composite substrate employed in the present invention offers theadvantage of allowing the devices to be pre-assembled, tested andrepaired prior to final attachment to the molded frame 12. In thepreferred embodiment, the cover plate 48 is formed from stainless steeland the thin laminate circuit 50 is a multilayered, thincopper/polyamide flexible circuit. However, materials other than thosedescribed above can be substituted for the cover plate 48 and the thinlaminate circuit 50. Alternative material choices for the cover plate 48include epoxy-glass PCB, molded plastic, glass, ceramic,ceramic-alumina, aluminum, silicon, silicon-nitride, carbon basedmaterials, copper-nickel alloys and other metal and non-metal rigid andsemi-rigid structures. The metal materials listed above offer advantagesover other material choices, because of their thermal transferproperties.

1. Anti-Static Embodiments

In applications involving static sensitive semiconductor devices,electrically emissive semiconductor devices or devices switching oroperating at frequencies above 50 MHz., the metal cover plate 48 canfunction as an electromagnetic shield or grounding plane by establishingan electrical ground potential across the cover plate. This is readilyaccomplished by direct electrical contact between one or more specificground contact pads 22 and the cover plate 48, or through groundconnections established through the thin laminate circuit 50. Additionalanti-static protection in selective locations can be provided byincluding anti-static or electrically conductive filler materials in themold compound when forming the molded frame 12 and/or adding specializedcoatings as part of a post molded process.

2. Battery Back-up

Referring now to FIG. 3, an embodiment is shown wherein a thin,rectangular battery 48A is substituted for the metal cover plate 48 ofthe composite substrate. In one embodiment, the battery 48A is the"Powerdex®" series of wafer-thin lithium batteries from Gould Inc.,Electronic Power Sources in Eastlake, Ohio. The battery is appropriatelyconnected in circuit with the semiconductor devices 54. The battery 48Ais preferably connected to the semiconductor devices 54 by electricalcontact between one or more specific ground and positive voltage contactpads 22, or through connections established through the thin laminatecircuit 50. A connection between the thin laminate circuit 50 and thebattery 48A can be achieved by electrical contact through conductivevias, windows, or an anisotropic conductive material, as describedelsewhere. The battery 48A is preferably controlled by a low-voltage orlow-current sensing device, for example, a device similar to thatidentified as part number MB 3790 available from Fujitsu Limited andFujitsu Microelectronics, Inc., Japan. This type of device monitorsin-circuit voltage/current levels and/or detects and regulates batteryrelated functions such as charging and discharging current flow. Whenproperly connected between the battery 48A and semiconductor devices 54,this embodiment enables prolonged data retention during intentional orunintentional interruption of the main power supply to the module, andis therefore particularly desirable for applications where the module isremoved and transported between operating platforms. The sensing deviceis preferably included inside the module as one of the semiconductordevices 54. Alternatively, the sensing device may be mounted on the maincircuit board.

3. Integral Components

Many applications require discrete resistors and/or capacitors (e.g. 56of FIG. 1) or bulk capacitance in close proximity to the semiconductordevices with which they are electrically coupled. In another embodiment,cover plate 48 is fashioned from a ceramic or silicon based materialwith internal capacitor plate structures, inductive and/or resistiveelements built into or on the surface which are electrically connectedto the laminate circuit, thereby eliminating the need for thesecomponents 56 from having to be individually mounted to the surface ofthe laminate circuit along with the semiconductor devices.

4. Integral Semiconductor Devices

In another embodiment, cover plate 48 is fashioned from a silicon orsapphire (alumina oxide) based substrate in which conventionalsemiconductor devices are constructed such as memory cells, logic gates,digital-to-analog, analog-to-digital converters and other functions asare commonly manufactured within the semiconductor industry. In thisexample cover plate 48 can function independently of additional elementssuch as a separate thin laminate circuit 50 and devices 54, or becombined with one or more of these and other elements as describedherein.

5. LCD Display

In yet another embodiment, cover plate 48 is fashioned from atransparent glass or plastic material compatible with liquid crystaldisplay (LCD) or active matrix and other display elements. Thisembodiment enables text or graphical information to be displayed for thebenefit of the user, such as information identifying the module type andconfiguration, amount and type of memory enclosed, or instructionsregarding battery status and module removal and replacement procedures,or display an index of stored data.

Thin Laminate Circuit

Numerous materials may be substituted for the thin laminate circuit 50without departing from the scope or spirit of the present invention. Forinstance, thin epoxy-glass PCBs, multi-layer ceramic circuits, screenprinted conductive inks or vacuum deposited and/or plated thin filmmetals such as: chrome/copper/gold, aluminum, lead/indium or otherevaporated metal and non-metal materials such as glass, opticaltransmissive fibers of glass or plastic and semiconductive materialscontaining doped and undoped regions and gallium arsenide (GaAs)materials as are commonly employed in the manufacture of semiconductordevices, and electrical insulative materials including polyamidecoatings or film, polyester film or "GoreTex™" laminates, are allalternative substitutes for the preferred thin laminate circuit. In someinstances, a film adhesive 52 may not be required. For example, a thinlaminate circuit 50 fabricated by sequential deposition ofcopper/polyamide thin films directly onto the cover plate 48 would notrequire an adhesive. These materials are preferred for high frequencyapplications associated with controlled or matched impedance circuitsemploying microstrip, stripline and/or wave guide structures as part ofthe laminate circuit.

The primary purpose of the thin laminate circuit 50 is to provideelectrical or optical interconnection between individual electronicdevices 54 and discrete components 56 or a group of stacked electronicdevices 52 (refer to FIG. 12) mounted on the circuit 50, and to conductdata signals and control voltages to and from the termination pads 34 or34' on the molded frame 12. To facilitate transfer of these signals andvoltages, a series of electrically conductive substrate pads 60 oroptical couplers (not shown) are arrayed along one or more edges of thethin laminate circuit 50 such that when subassembly 32 is attached tothe molded frame 12, substrate pads 60 and/or optical couplers overlayor align and connect with corresponding termination pads 34 or opticalcouplers on the molded frame 12. Voltage and data signals applied totermination pads 34 or optical couplers are connected through substratepads 60 or optical couplers of the thin laminate circuit 50 and carriedthrough multiple lines and traces or optic fibers residing on thesurface or placed within internal levels of circuit 50 to surface bondpads 76 or optic terminations that surround or underlay individualsemiconductor devices 54 and passive components 56. Devices 54 andcomponents 56 are in turn electrically and/or optically connected tobond pads 76 or optic terminations on the laminate circuit 50. In thismanner, semiconductor devices and passive components are connected incircuit and are able to exchange data, control signals and voltagesbetween one another and between contacts 22 arrayed along one or moreedges of the molded frame.

As previously described, other embodiments, which employ a cover plate48 fashioned from a silicon or sapphire based substrate(s) with integralsemiconductor devices, would not require a separate thin laminatecircuit 50. Device interconnects, substrate pads 60, and/or opticalcouplers in these embodiments, would be incorporated into or upon thecover plate material itself.

1. Thermal Enhancements

In the preferred embodiment, the semiconductor devices 54 and discretecomponents 56 are attached to the surface of the thin laminate circuit50, requiring any heat generated from the devices to pass throughcircuit 50 and adhesive 52. To lower thermal resistance and, hence,enhance thermal conduction of the heat generated by the semiconductordevices contained inside the module to the exterior surface of themodule, several features can be incorporated as part of the thinlaminate circuit 50 or cover plate 48. Maximum thermal conduction isachieved by incorporating open windows 62 within the thin laminatecircuit 50 and if present, adhesive 52, to allow backside chipattachment directly to the cover plate 48, as shown in FIG. 4. Chipattachment can be accomplished using eutectic alloying materials (e.g.,solder), metal filled epoxy or other thermally conductive adhesives.

An alternative approach to lower thermal resistance makes use of smallthermal vias 64 illustrated in FIG. 10, formed as an integral part ofthe thin laminate circuit 50. Strategically arrayed under selective chipmounting sites, as shown in FIG. 10A, these structures consist of solidconductive posts or channels through circuit 50 and if present adhesive52, into which a thermally conductive material is emplaced. Intimatethermal, metal-to-silicon, contact is then established between the coverplate 48 and semiconductor device 54 at localized areas beneathsemiconductor devices 54.

Another enhancement for improving thermal convection, or transfer ofheat into the ambient air surrounding the module, involves theincorporation into the external surface 48' of the cover plate 48, aknurled surface finish 66 or uniform array of small, multi-tiered,polygon structures 68, for the purpose of increasing the total externalsurface area of cover plate 48, as illustrated in FIGS. 11, and 29-30.

In yet another embodiment of this invention, cover plate 48 and frame12, alone or in combination, can be manufactured to contain multiplecompartments or channels through which gas or liquid coolant materialscan be circulated to effectively distribute or remove heat generatedfrom contained semiconductor devices. For instance, a miniaturecryogenic pump (not shown) can be fashioned into cover plate 48,consisting of an enclosed expansion chamber connected to small entranceand exit channels that closely parallel one another in a sinuous path.When a gas (air, nitrogen, etc.) is introduced from an appropriate highpressure source or generator through the entrance channel into theexpansion chamber, a localized pressure drop caused by rapid expansionof the gas results in an associate temperature drop of the gas. Whenre-circulated out an exit channel placed in close sinuous proximity tothe entrance channel, the cooler exit gas conducts heat from incominggas and progressively lowers the temperature of the cover plate 48.Alternatively, cover plate 48 may be fashioned as a thin "heat pipe" inwhich an appropriate fluid or gas is contained and self-circulated byfluid/gas dynamics caused by conversion of the fluid or gas into a stateof lower density upon contact with a high heat generating source andconsequent movement to a cooler region of the cover plate or extensionthereon and subsequent recondensation or re-densification upon exchangeof the latent heat into ambient air or other cooling material.

2. Optical Signal Communication

Signal communication between adjacent devices 54 and/or opposingsubassemblies 32 will typically be accomplished through electricalconduits of lines and traces embedded in or fashioned on the thinlaminate circuit 50. However, since it is expected that semiconductor orother electronic devices employing light emitting/receiving structureson their respective surfaces or edges will eventually become practicalalternatives for chip-to-chip communication, this invention provides acompact, "light-tight" enclosure for shielding these components. Withthis application in mind, point-to-point, data/signal transmission canoccur across the narrow air gap between juxtaposed semiconductor deviceswhich are accurately aligned or positioned in a face-to-face,edge-to-edge or other configuration with one another, therebyeliminating the necessity for long crossover electrical paths (21,37-39, 51, 51A, 53, and 78) through the thin laminate circuits 50 andacross the stepped ledge 30 or edges 20.

Therefore, in an alternate embodiment, the semiconductor devices onadjacent or opposite surfaces of subassemblies 32 transmit and receivedata or signals through light emitting and/or light sensing elements ofthe semiconductor device(s) itself. In this embodiment, the protectiveovercoat compound is eliminated or optically transparent or transmissiveat the wavelength frequency of the light. To enhance light transmissionbetween such semiconductor devices, a solid glass or semi-rigid plasticor elastic or resinous polymer or other material exhibiting fiber-opticlike properties is molded, injected, coated, dispensed or applied as afilm to bridge the gap between such semiconductor devices within thismodule and to conduct the light in essentially unidirectional ormulti-directional paths.

In yet another embodiment, the subassembly cover plate 48 or substrate50, alone or in combination, is an alternate source for the lightemitting and light receiving elements. In other words, structures areembedded in or on the surface of the substrate and/or cover plate whichtransmit and/or receive light. Such structures include gallium arsenide(GaAs) coatings or deposits over silicon, polysilicon, alumina nitrideor oxide, or optically transparent glass or plastic, to produce photodiodes, or other light emitting (LED) and light receiving/sensingdevices. The cover plate may be the source for the lightemitting/sensing elements while an otherwise optically transparentsubstrate may contain electrical conductive elements. Likewise, thecover plate may contain electrical conductive elements while thesubstrate may be the source for the light emitting/sensing elements.

Subassembly(s) Attachment to the Module Frame or Module Frame ConnectorSocket

Electrical and mechanical mating between the subassembly(s) 32 and themodule frame 12-12C and/or module frame socket 12D-12K is accomplishedby one of several methods. In the preferred embodiment, an anisotropic,electrically conductive, adhesive film 58, available from severalmanufacturers, is used. This material characteristically conductselectrical current perpendicular to the plane of the film in a directionacross its thickness, but is essentially non-conductive in directionsparallel to its planes. This material is pre-positioned as either adry-film preform or can be dispensed through a syringe, or stenciled ortransfer stamped in a liquid state, then dried in place on either pads60 of subassembly 32 or pads 34/34' of molded frame 12. Electrical andmechanical attachment is then accomplished by applying thermal energyand/or exerting pressure between the mating surfaces in accordance withthe manufacturer's instructions. Alternatively, a solderable alloycombined with a contact or thermal setting adhesive may be selectivelyapplied as described above and thermally, sonically, or pressureactivated to effect both a mechanical and electrical interconnection.Yet another material that is suitable is commonly referred to as a`z-axis elastomeric conductor`, fashioned from a material with adhesiveproperties to effect simultaneous mechanical and electrical attachmentbetween the subassembly 32 and the molded frame 12. Yet another methodmakes use of molded appendages, slots, holes, ribs and/or structures onthe molded frame that can be sonic welded or thermally deformed toattach subassembly 32 to molded frame 12 and establish electricalcontact or optical coupling between pads 60 or optical couplers ofsubassembly(s) 32 and pads or pins 34/34' or optical couplers of moldedframe 12. In other embodiments of the module wherein the subassembly(s)are intended to be semi-permanently attached (i.e. removable) to amodule frame socket (FIGS. 12D-12K), the subassembly(s) are pressed orslid into position over the socket and held in mechanical, electrical oroptical contact by means of a pressure or friction fit between themating surfaces. Molded features residing on the molded module frame 12and/or module frame socket can be employed to capture and secure themodule within or against the socket through multiple means includingspring, wedging, and/or pinching action exerted against the contact padsor pins. These and other features are illustrated and discussed belowwith reference to FIGS. 19, 22, and 26-30.

Device Attachment

Semiconductor device attachment to the thin laminate circuit 50 isachieved by one of several methods commonly known and available with theindustry. Tape Automated Bonding (TAB) technology provides a network oftab leads 72 attached to metallurgical bumps formed at specific bondpadsites 76 of the semiconductor device. TAB leads connected to the bumpsare elevated from the surface and extend beyond the perimeter of thesilicon device, as partially shown in FIG. 4. The free ends of the TABleads may be mechanically/electrically bonded to appropriately spacedand metallurgically compatible bond pads 76 (ref. FIG. 10) on thelaminate circuit 50 with the silicon device(s) placed in either aface-up or face-down configuration. Alternatively, the devices areattached using `Chip On Board` (COB) technology where the chip ismounted with an epoxy paste or solder alloy in a face-up orientation,and electrically connected to the laminate circuit 50 with conventionalwire-bonds 73 as illustrated in FIGS. 18A-18C, and 24. Yet another, andpreferred technique, shown in FIGS. 2, 3, 10, 12, 14-16, 18D, 21-23, and26-29A, is known as Flip Chip Assembly or Direct Chip Attach (DCA). Inthis example, suitably placed and sized bond pads 74 on the face of thesemiconductor chip(s) are directly attached and electrically connectedto matching bond pads 76 on the laminated circuit 50 through one ofseveral techniques and material choices. Examples include, but are notlimited to: `Controlled Collapse Chip Connection` ("C4") solderingtechnology developed and licensed by IBM, conductive epoxies andpolymers, solder-ball reflow, anisotropic conductive adhesives, aspreviously described, and metallic coated, raised, silicon orsilicon-carbide structures such as those developed by Elm Technology ofSanta Barbara, Calif. The aforementioned structures are designed topierce oxidation coatings of either pad site and effect a permanentelectro/mechanical bond between the semiconductor device and laminatecircuit. Other micro-machined or etched structures can be formed on thepad surfaces to permit a "Velcro"-like electro/mechanical attachment ofthe semiconductor device to the laminate circuit. Typically these chipmounting methodologies are combined with specific chip undercoating orovercoating materials to enhance mechanical reliability, hermeticityand/or thermal conductivity. [Note: In some instances of device mountingmethodologies, it is preferable that cover plate 48 and thin laminatecircuit 50 be selected from materials exhibiting coefficient of thermalexpansion characteristics, either independently or in combination, whichmatch or approximate that of the chip devices attached thereon topromote better mechanical reliability of the attachment bondline.]

Device Types

As shown in any of the various embodiments, a variety of semiconductordevices 54 are readily assembled into the module of the presentinvention. Typical devices include, but are not limited to, Memory chips(DRAM, AS-DRAMs, Flash-EEprom, ROM, Fast/Slow-Static RAMs,Ferro-electric RAM, et. al.), Microprocessor, Application Specific IC's(ASICs), Gate Array devices, Telecommunication IC's and othersmanufactured in CMOS, BiCMOS, GaAs and other technologies compatiblewith TTL, ECL, FAST and other logic interface standards. Typicalapplications in which this invention would find usage include mainmemory storage or digital and analog signal processing for devices suchas: handheld personal digital assistants (PDA's), sub-notebook andnotebook sized computers, desktops, workstations, mainframes,file-servers, and super-computers, and other graphic intensiveapplications, such as high definition television (HDTV), "on-demand"video storage and server units, handheld personal communication anddata/information display devices.

In the various embodiments, the semiconductor devices 54 are notpreencapsulated, but rather comprise "bare" silicon die. In other words,silicon die are attached directly to the composite substrate. Thesemiconductor devices are not prepackaged with TSOP or SOJ-type moldedpackages.

1. Stacked Memory Chips

In some high performance applications, such as for super-computers, aneven higher packaging density can be achieved by combining thisinvention with stacked memory chips 52, to produce another embodimentdetailed in FIG. 12. Stacked memory chips 52 are available, for example,from Irvine Sensors Corp. of Costa Mesa, Calif. and IBM at its facilityBurlington, Vt. These stacked chips are pre-processed through a waferback-lapping operation, to substantially reduce the device thickness,before the individual chips or wafers are glued together to form short,vertical, interconnected, 3-D memory stacks. These memory stacks canthen be directly face-bonded (DCA or Flip Chip mounted) or otherwiseconnected to the thin laminate circuit 50 as described above. Thisembodiment is also warranted for applications in which volumetric spaceis extremely limited.

In an alternate embodiment of this invention, illustrated in FIG. 12A,cover plate 48 may be fashioned from several thin sections of siliconwafers 55, each section containing multiple devices interconnected fromdevice-to-device within a specific section, and each section in turnlayered on top of one another and interconnected from layer-to-layer bymeans of metal or other electrical conductive material and/or opticalcoupling across the edges of the resultant stack of wafer sections orthrough vias etched or abraded through the wafer sections. The resultantcover plate can then be attached to the molded frame or module socket asdiscussed herein. Elements 56 are preferably used as decouplingcapacitors.

2. Security Devices

Microprocessors and memory chips are relatively expensive. Sincemultichip modules can contain a number of these devices in a compact,easily hidden and transported package, and in particular the thinmultichip module described herein, these products are expected to betargets for high-tech crime. Consequently, a unique and potentiallyimportant embodiment of this invention is the inclusion of anti-theftdetection and/or location devices within the module to aid recovery orrender the modules inoperative for unauthorized usage. A variety ofsecurity devices can be incorporated within the module as one of thesemiconductor devices 54 to emit detection signals in response toscanning hardware or require a user-specified access or encryption codeto properly function. These security devices are preferably implementedas an ASIC comprising one of the semiconductor devices 54 in any of thevarious embodiments. These security devices are accessible only bydisassembly, which essentially destroys the module.

Passive Components

In addition to the variety of semiconductor devices that findapplication in this invention, associated passive electronic components56, including chip capacitors, resistors, etc., can also be surfacemount soldered onto the thin laminate circuit. Chip decouplingcapacitors are used in particular with memory devices to function in thesuppression of spurious voltage spikes when electrically connectedbetween a net positive or negative voltage reference and electricalground. For some applications, these passive components 56 will standslightly above the mounted height of the adjacent semiconductor devices54, as shown in FIGS. 2, 3, 10A, 13 and 17. Since these components aregenerally composed of a robust ceramic material, they can beadvantageously employed to prevent direct pressure from being appliedagainst the fragile semiconductor devices should the assembled module becompressed in an axis perpendicular to the outer surface(s) ofsubassembly(s) 32. Alternatively, special raised stand-off features canbe integrally molded into the floor 28 or across the cavity of themolded frame 12 to prevent damage resulting from compressional forces.Alternatively, the semiconductor devices would be protected through theaddition of an overcoated plastic compound as described below.

Multiple Subassemblies

Referring now to FIG. 13, an embodiment of the present invention whichincludes a frame having cavities 28 on opposite sides of the frame 12Bis shown. Only one cavity is shown in FIG. 13, the cavity 28 on theother side of the frame being hidden in this view. A substratesubassembly 32 mounts in each of the respective cavities as shown. FIG.14 is a cross-sectional view of FIG. 13. FIGS. 14A and 14B are alternateembodiments of FIG. 14 with a different molded frame 12 that places thesubassemblies 32 further away from the center line of the molded frame12, thus allowing more spacing for internal components.

As shown in FIG. 14B, a second thin laminate circuit 50 is attached tothe floor 28 of the molded frame 12 in addition to the thin laminatecircuit 50 on the cover plate(s) 48. Tab leads 106 or pads arrayed alongthe edge(s) of this extra circuit 50 are electrically connected toappropriately sized and positioned termination pads 34 located along anadditional stepped ledge adjacent the floor 28, or to a row of contactsspaced along the floor 28 of the molded frame 12. An additionalplurality of semiconductor devices 54 are optionally mounted to thissecond thin laminate circuit 50. Another embodiment,--principallysuitable for a molded frame 12 formed from multiple, stacked, layers ofkiln-fired, ceramic sheets imprinted and interconnected withelectrically conductive lines, vias and pads,--can incorporate thecircuit as an integral part of the floor 28 of the module frame 12, suchthat the uppermost layer constitutes the device and component attachmentsurface. In these embodiments, semiconductor devices 54 can be attachedto the first laminate circuit 50 as discussed in connection with FIG. 1and a second set of semiconductor devices 54 can also be connected tothe second laminate circuit integrated into the floor 28.

In yet another embodiment similar to FIG. 14B, a thin printed circuitboard (PCB) may be substituted for floor member 28 upon whichsemiconductor devices 54 can be mounted. This embodiment is particularlycompatible with memory card devices that conform or are similar in form,fit, or function to those standardized by the Personal Computer MemoryCard International Association of PCMCIA. In this embodiment, additionaldevice mounting surfaces made available with the addition ofsubassemblies 32 enable a doubling of available component capacity orprovide for a better thermal management of heat sensitive or producingdevices than current PCMCIA type cards. It is noted that this embodimentis made compatible with present PCMCIA cards, by modifying the moldedmodule frame 12 to include female receptacle contacts along the shorteredge of the frame. It is also noted that FIGS. 14, 14A and 14B are notdrawn to scale, and sides 20 of the molded frame 12 preferably have thesame thickness in FIGS. 14, 14A and 14B, although this is not required.

Referring now to FIGS. 15, 15A, and 16, alternate views of thesemiconductor module illustrated in FIGS. 14 and 14A are shown. FIG. 15is a cross-sectional view of an embodiment of the molded frame shown inFIG. 6 and is similar to the module view shown in FIGS. 14 and 14Aexcept that the subassembly in FIGS. 15 and 15A are in a final assembledconfiguration. The cross-sectional view illustrated in FIG. 15emphasizes the plastic portion of the molded frame 12 and the stamped oretched metal contact 38 is substantially hidden. FIG. 15A is across-sectional view emphasizing the metal contact 38 portion of themolded module frame 12. FIG. 15 A also illustrates an additionalinterconnection 78 at the stepped ledge or edge of the molded frame 12opposite the contact 38 end enabling a cross-over electrical pathbetween the laminate circuits 50 across the stepped ledge or edge. FIG.16 is similar to the view illustrated in FIG. 15A except that a singleflexible laminate circuit 50 that is folded at one end 51 is substitutedfor the two laminate circuits 50 and interconnection 78 of FIG. 15A.

Therefore, in summary, in embodiments where two or more compositesemiconductor substrate subassemblies 32 are attached to the moldedframe 12, as shown in FIGS. 13-16 the floor 28 can be reduced inthickness and repositioned along the center-line axis to increase theavailable spacing between mounted devices and components.Substrate-to-substrate electrical interconnect is normally provided viaelectrical shunting 21 of the contact pads 22 across the bottom edge 20of the molded frame 12 as previously described in FIG. 5, or throughstamped or etched metal contacts 37, 38, or 39. However, additionalinterconnections can be facilitated around the entire perimeter of theinternal stepped ledge 30 or edge of molded frame 12 opposite contacts22 or 22' (i.e. top edge or side of frame), through metal contacts 78 asillustrated in FIG. 15A, or through a single continuous flexible thinlaminate circuit 50 folded over at the top 51 of the module asillustrated in FIG. 16 (refer also to FIGS. 18B-D, and 20-30). Flexiblethin laminate circuit can also be attached as a separate piece 51A tosubassemblies 32 as illustrated in FIGS. 20 and 21, or can be foldedover and around the bottom edge 53 of the module as illustrated in FIGS.18A and 25B-28A or as discussed below.

Module Removably Connected to a Module Frame Socket

In the above embodiments including variants employing multiplesemiconductor substrate subassemblies 32, the module includes apermanently attached molded frame 12 having a single internal cavity 14or two internal cavities separated by a floor 28 as described above.Semiconductor devices 54 are mounted to the respective subassembly(s)and are received in the respective cavities, preferably not contactingthe floor of the respective cavities except as illustrated and discussedwith respect to FIG. 14B. In other embodiments, such as overcoatedembodiments discussed below with reference to FIGS. 17, and 18A-D, andFIGS. 21-30, the module does not include a permanently attached moldedframe as part of the module itself, but rather is adapted for insertioninto a module frame socket, which essentially behaves as the moldedmodule frame, i.e. the module frame socket establishes electrical and/oroptical and mechanical connection to the subassembly(s) and addsrigidity to the module. As shown in FIG. 19, the module frame socket 12Dis permanently attached to the main circuit board instead of thesubassembly 32 and provides mechanical and electrical connection betweenthe removable subassemblies and the main circuit board.

Overcoated Embodiments

In yet another embodiment of the present invention, subassembly 32 isassembled independently of the molded frame 12 by applying or molding aprotective overcoat 70, as shown in FIG. 17. As shown in FIG. 17A-B, thesubassembly comprises a composite substrate 46 preferably includingcover plate 48 and thin laminate circuit 50 that is bonded to the coverplate 48 by film adhesive 52. A plurality of semiconductor devices 54and passive components 56 are mounted on the laminate circuit 50. Theprotective overcoat 70 comprises an epoxy resin, thermal plasticencapsulant or similar mold compound or plastic laminate film and coversthe semiconductor devices 54, passive components 56 and substantialsurface of the thin laminate circuit 50, while leaving substrate pads60, end surfaces 102 (optional) and external surface 48' of the coverplate 48 exposed. As illustrated in FIG. 19, the resultant subassembly32 can then be mated to an appropriate molded module frame socket 12Dwith slots to receive the end surfaces 102, or combined with a pluralityof leads 40 or 40' (FIG. 9) for direct mounting to a main circuit board.Alternatively, subassembly 32 could be completely encapsulated by theprotective overcoat 70 leaving leads 40 or 40' protruding from the edge.Other overcoated embodiments are discussed below.

Double-sided Subassembly

Each of the aforementioned subassemblies 32 use only one of twoavailable surfaces of cover plate 48 to attach the thin laminate circuit50 and devices 54. Turning now to FIGS. 18A-18D, additional embodimentsof the module shown in FIG. 17 are illustrated in which additionalsemiconductor devices 54 and other components 56 are attached to theexternal surface 48' (FIG. 17B) of the cover plate 48. In theseembodiments, an additional or second thin laminate circuit 50 is appliedto at least a portion of the external surface 48' of the cover plate 48,and a second plurality of semiconductor device 54 and passive components56 are mounted to either the second laminate circuit 50 or directly tothe cover plate 48. A protective overcoat 70 is applied or molded to thesurface 48'. In this embodiment, protective overcoat 70 functions inpart as the molded frame providing rigidity to the module. Theprotective overcoat 70 also serves to encapsulate this second side ofsubassembly 32. In one sense, the protective overcoat molds around thesubassembly, thereby essentially creating a "cavity" around thesubassembly 32. The cover plate 48 no longer functions as a cover butcontinues to function as a thermal conductor while also acting as arigid mounting surface for semiconductor devices 54 and components 56.Thin laminate circuits 50 on either surface of cover plate 48 can beeither physically separate and, therefore, electrically independent, orphysically and electrically joined along the edge(s) of cover plate 48as a single flexible circuit folded over and around said edge(s). Inthese examples, the module preferably appears symmetrical with respectto a centerline drawn end-to-end through cover plate 48, as viewed inFIGS. 18A-18D. Other applications make use of a flexible circuit foldedover and around the edge(s) of cover plate 48 and extending only partway onto surface 48', to provide an additional row or rows of substratepads 60 as illustrated in FIGS. 25B, 26-28.

FIGS. 18A and 18B comprise the cover plate 48 and semiconductor devices54 which are mounted on either side of the cover plate 48, as shown. Thesemiconductor devices 54 are preferably mounted to laminate circuits 50which are applied to opposite sides of the cover plate 48. In FIG. 18A,flexible circuit 50 is applied, preferably as a single sheet, foldedover and around the bottom edge of cover plate 48 at one end, as shownat 53 and extending to the edges of the other end. FIG. 18B illustratesthe flexible circuit 50 folded over and around the opposite or top endof the cover plate 48, as shown at 51. In FIGS. 18A and 18B, theflexible circuit 50 and adhesive film 52 have one or more open windows62 through the flex circuit and adhesive film 52 similar to thatillustrated in FIG. 4. The semiconductor devices 54 are preferablymounted in the windows of the flexible circuit. It is noted that theflexible circuit 50 surrounds the semiconductor devices 54, althoughthis is not illustrated in FIGS. 18A-B due to the cross-sectional view.In other words, a different cross-sectional view taken through a part ofthe module between the semiconductor devices 54 would show a singlecontinuous thin laminate circuit 50 beginning at an edge on a first sideat a first end and extending across the first side, folded over thesecond end and extending across the second side returning to the firstend.

In FIGS. 18A and 18B, substrate pads 60 and bonding pads 76 are mountedon either side of the outside surface of the flexible circuit 50. Thebonding pads 76 connect to the semiconductor device bond pads 74 withconventional wire bonds 73, as shown. The bonding pads 76 are in turnelectrically connected to other bonding pads 76, or substrate pads 60,through conductive lines and traces routed across the surface orinternal laminate layers of circuit 50. In FIG. 18A, conductive tracesare also routed across the folded end 53 of flexible circuit 50 toprovide electrical connection between other substrate pads 60 on theopposite surface. In FIG. 18B, electrical connection between thesubstrate pads 60 are provided through an electrical trace(s) at foldedend 51. However, this requires a long signal path routed over and acrossthe top end of the module and back down the opposite side. In oneembodiment, a conventional epoxy-glass PCB (not shown) is substitutedfor the flexible circuit 50 and cover plate 48, and electricalconnections between contact pads 60 are achieved using plated via holespassing through the circuit board thickness. A protective overcoat 70,preferably comprised of a thermal plastic encapsulant, encases thesemiconductor devices on both sides of cover plate 48 in FIGS. 18A and18B.

In FIGS. 18C and 18D, the module comprises the cover plate 48 with theflexible circuit 50 substantially surrounding the cover plate 48, asshown. The semiconductor devices 54 mount on either side of the flexiblecircuit 50. In FIG. 18C, thermal vias 64 are positioned in the flexiblecircuit 50 between the cover plate 48 and the semiconductor devices 54and provide thermal conduction of the heat generated by thesemiconductor devices 54 to the cover plate 48. It is noted in FIG. 18Cthat thermal vias 64 are provided instead of open windows 62 in thisembodiment and that semiconductor devices 54 sit atop flexible circuit50. In FIGS. 18C and 18D, flexible circuit 50 is applied as in FIG. 18B,i.e., folded over and around the top end of the module. FIG. 18Dillustrates an embodiment in which a thin rectangular battery issubstituted for cover plate 48, as previously discussed with referenceto FIG. 3. Also in FIG. 18D, bondpads 74 of the semiconductor devices 54are attached to the bond pads 76 of the flexible circuit 50 using FlipChip Assembly or Direct Chip Attach (DCA), as discussed above.

Folded Subassemblies

Referring now to FIGS. 20-30, alternate embodiments of the presentinvention are shown. As previously referred to in FIG. 16, and nowfurther illustrated in FIG. 20, these embodiments include a fold overdesign and do not include a molded module frame as part of the module,but rather are adapted for connection to a module socket similar to thatshown in FIG. 19.

1. Protective Overcoat Material

These embodiments also preferably include a protective overcoat 70A toencapsulate the semiconductor devices 54 and components 56 mounted uponcomposite substrates 46, and thereby protecting them from environmentalhazards including atmospheric moisture, surface contamination, orstresses transmitted through the module, and aiding in the overallrigidity of the module. Protective overcoat 70A can consist of the samematerials as previously mentioned in reference to the protectiveovercoat 70 used in FIGS. 17-18D. In these examples, however, thedevices 54 and components 56 face inward toward a central cavity 14,similar to FIGS. 1-16, and are substantially protected by cover plates48. Therefore, less rigid or semi-rigid compounds can be substituted forprotective overcoat 70A, which are intended to function more as acushioning agent to fill the gap or void existing between adjacentsubassemblies 32. Examples include elastomeric materials, and otherflexible rubber-like compounds that could be injected, molded, ordispensed to encapsulate the devices either before or after thesubassemblies are folded together. In some embodiments (FIGS. 22-24, 29Aand 31) virtually all of the volumetric void between adjacentsubassemblies 32 is filled with protective overcoat 70A. This wouldtypically be accomplished by dispensing overcoat material 70A into thecavity after subassemblies 32 are folded together. In other embodiments(FIGS. 21 and 26-28) cavity 14 is only partially filled with overcoatmaterial 70A, which indicates the overcoat material 70A was molded orapplied before subassemblies 32 were folded together. It should benoted, that these Figures are not to scale, and that little or no spacemay exist for FIGS. 21 and 26-28 in actual usage dependant upon spacingrequirements dictated by the module socket into which these modules areinserted.

In addition to improving the overall rigidity and mechanical integrityof the finished assembly, protective overcoat 70A also improves thehermeticity or moisture resistance of the module. Additionalmanufacturing steps to improve hermeticity at the component orsemiconductor device level include special chip surface coatings orundercoatings--depending upon device orientation and applicationmethodology--including, but not limited to organic epoxies (ex. "Praleen™," die undercoating adhesives, etc.), vacuum/plasma deposited ceramicor diamond coatings, moisture immobilizing polyamide and other suitablematerials known within the industry.

Referring now to FIG. 21, two subassemblies 32 are illustrated incross-section joined with a separate piece of folded laminate flexcircuit 51A at the end opposite from the substrate pads 60. First andsecond cover plates 48 connect to the flex circuit 51A. First and secondlaminate circuits 50 are applied to inner surfaces of the first andsecond cover plates 48 respectively. First and second pluralities ofsemiconductor devices mount on the first and second laminate circuits50, respectively. Semiconductor devices 54 are attached to the surfaceof laminate circuit 50 by one of several Direct Chip Attachedmethodologies discussed above. A protective overcoat 70A partially fillsthe void or cavity 14 enclosed by the opposing subassemblies 32 andfolded flex circuit 51A. In this embodiment, the cover plates 48 arediscontinuous or separated, but are joined together along one or moreedges to each other through the laminate flex circuit 51A, enabling thesubassemblies 32 to be folded such that the semiconductor devices areplaced in the interior of the module, as illustrated in FIG. 21. In analternate embodiment of the invention, the subassemblies 32 are reversefolded about the flex circuit 51A such that the semiconductor devicesare positioned on the outside surfaces of the respective cover plates48. This embodiment is similar to FIGS. 18A-D except that in thisembodiment the first and second pluralities of devices 54 are mounted tofirst and second cover plates 48, whereas in FIGS. 18A-D the first andsecond pluralities of semiconductor devices 54 are mounted on oppositessides of the same cover plate 48. Although any included angle betweenthese two extreme configurations can be used for the practice of thisinvention, the preferred orientation is as represented in FIG. 21 foradvantages as previously discussed.

2. Module Frame Socket

Referring now to FIG. 22, an alternate embodiment of FIG. 21 is shown incross-section, poised above a molded module frame socket 12E configuredas a receptacle to receive the bottom edges of subassemblies 32. In thisembodiment and those represented in the following FIGS. 23-30, as withFIGS. 17, 18A-D, 20, and 21, subassemblies 32 are semi-permanentlyattached (i.e. removable) to a module frame socket (12D-K), being heldin place by some form or combination of pressure/friction fit, pinching,wedging or spring action pressure exerted between contact pads 34/34' ofthe module frame socket and composite substrate pads 60, or secured bymolded features or structures residing on the molded frame of the modulesocket. Some of these structures may be moveable by means such as arotating or sliding cam action or sliding wedge or lever-actuatedclamping motion or heat/voltage actuated bi-metal device effecting aclamping or pinching action to allow subassembly(s) 32 to be morereadily engaged or disengaged from its module frame socket 12. Thesemoveable structures would effectively reduce or eliminate the pressureexerted between contacts 34/34' of the module frame socket and contacts60 of subassembly(s) 32 when mating or un-mating these parts.

Referring again to FIG. 22, subassemblies 32 are joined with acontinuous layer of flex laminate circuit 50 folded over at the top 51,and backed with a continuous layer of cover plate 48. In this instance,cover plate 48 is presumed to be composed of malleable or ductilematerial thin enough to enable folding of the material without breakage.The interior cavity in this example is substantially filled (i.e. mostof the cavity is filled) with a protective overcoat material 70A. Moduleframe socket 12E, also shown in cross section, is depicted with stampedmetal contacts 39' similar to those previously discussed in FIG. 8. Itis noted that this view of module socket 12E is a cross-sectional view,and that module socket 12E appears substantially the same as the socketsillustrated 10 in FIGS. 19 and 29.

FIG. 23 is another embodiment of a module similar to that shown in FIG.21, with exception that subassemblies 32 are joined with a continuouslayer of flex circuit 50, and the interior cavity is substantiallyfilled with protective overcoat material 70A like FIG. 22. In analternate embodiment (not shown) of FIG. 21 or 23, contact pads 60 canbe formed across the outside surface of folded thin laminate circuit at51 or 51A for engagement with a module frame socket similar to 12Fillustrated in FIG. 26. In this instance the module would be mountedupside down with respect to other embodiments detailed in FIGS. 22-30.In yet another embodiment of FIG. 21 (not shown), thin laminate circuit50 may extend beyond the edges of the composite substrate, such thatcontact pads 60 are not supported by the cover plate 48, but are part ofa flexible circuit that can be flexibly positioned at a variety ofangles for interfacing with an appropriate module socket or for directplacement against the main circuit board.

FIG. 24 is yet another embodiment of a module similar to that shown inFIG. 22, with exception that the laminate flex circuit 50 has windowopenings 62, similar to 25 those represented in FIG. 4 and thesemiconductor devices 54 are positioned in the window openings. Thesewindow openings 62 enable the semiconductor devices 54 to be attacheddirectly to the cover plate 48 for optimum thermal dissipation orconduction. Semiconductor devices 54 are connected to the laminate flexcircuit 50 by wire bonds 73.

FIG. 25 is a top view looking down on a module similar to FIG. 23 as itwould appear prior to being folded and/or encapsulated with protectiveovercoat material 70A. Line B-B' represents the fold axis as viewed fromabove. FIG. 25A is a cross-section view taken from FIG. 25 at thelocation represented by the arrows. FIG. 25B is another embodiment ofFIG. 25A, in which the laminate flex circuit 50 is folded over andaround the bottom edges 53 to provide another set of substrate pads 60on the opposite side 48' of cover plate 48 similar to those representedin FIG. 18A.

The modules represented in FIGS. 26, 27 and 28 are similar to oneanother, and are cross-section views of yet another embodimentresembling FIG. 25B, with exception that multiple rows of substrate pads60 are depicted on both sides of the bottom ends of subassemblies 32.These figures also illustrate several alternative types of module framesockets that can be adapted to the module. For example, as shown in FIG.26, a cross-sectional view of an embodiment of FIG. 25B is shown inwhich multiple rows of contacts 60 are provided by a single continuousthin flexible laminate circuit 50 folded over at the top 51 and aroundthe edges 53 of opposing subassemblies 32. The resultant assembly isshown superimposed above a cross-sectional view of a module frame socket12F that is wrapped with a corresponding flexible laminate circuit 50'.As shown in FIG. 27, a cross-sectional view details the embodiment ofFIG. 26 in which contacts 60 along the edges of opposite and opposingsubassemblies 32 are mated to a module frame socket 12G exhibitingmultiple independent contacts 34'/37'. As shown in FIG. 28, across-sectional view details the embodiment of FIG. 26 in which contacts60 along the edges of opposing subassemblies 32 are mated to a moduleframe socket 12H exhibiting independent 34' and bifurcated 34" orredundant contacts. Upon insertion of subassemblies 32 into module framesockets 12F, 12G, and 12H, these contacts (34, 34', 34") would alignwith those on subassemblies 32, and establish electrical connection tothe main circuit board (not shown).

Referring now to FIG. 28A an alternate embodiment of the module shown inFIG. 26 is illustrated. In this embodiment, the flex circuit is foldedthree times as in FIG. 26, but extends all the way across respectivesubassemblies for mounting of additional semiconductor devices. The flexcircuit has a principal fold at 51 and is also folded at points 53. Aswith FIG. 26, multiple rows of contacts are provided at the folds 53 ofthe single flexible circuit 50. As with FIG. 26, semiconductor devices54 are mounted to the interior of the module on the flex circuit, asshown. However, in FIG. 28A, additional pluralities of semiconductordevices 54 are mounted on the outside of the respective cover plates onthe laminate circuit 50. Therefore, in the embodiment in FIG. 28A, foursets or pluralities of semiconductor devices are mounted to the module.First and second pluralities of semiconductor devices are mounted on theinterior of the module to the flex circuit applied to the interior ofthe respective cover plates 48. Third and fourth pluralities ofsemiconductor devices are mounted to the flexible circuit 50 which isapplied to the exterior surfaces of the cover plates 48. A protectiveovercoat 70A is applied over each of the four pluralities ofsemiconductor devices as shown.

FIG. 29 is a perspective view of the module previously depicted in FIG.23, showing how it would slide over and straddle stepped ledges 30 ofmodule frame socket 12I, until seated near the bottom edge of frame 12I,as illustrated in cross-section 29A. In this example, module framesocket 12I is permanently attached to the main circuit board andsubassemblies 32 are temporarily attached or inserted (i.e. removable asrequired) on to frame socket 12I.

FIG. 29B is a cross section view of another alternate embodiment of FIG.29A in which a `z-axis`0 conductive elastomeric material 81 is theprinciple means for establishing electrical contact between the maincircuit board (not shown) and contact pads 60 of the subassembliesthrough module frame socket 12J.

FIG. 30 is another perspective view of an embodiment similar to FIG. 29,with exception that contacts along the bottom edge of molded frame 12Kare equivalent to those previously discussed in FIGS. 6, and 15-16.

Conclusion

The improved multichip module of the present invention offers numerousadvantages over the prior art. For example, the present inventionprovides a significant decrease in cross-sectional thickness and overallweight reduction for the module as a whole, thereby improving the totalnet packing density and making the module more appealing forlight-weight, thin, portable, hand-held applications. As previouslydiscussed, since this invention is approximately one-third of thethickness of a standard SOJ-type SIMM, it is feasible to mount two orthree times more component modules within a specified area of thecircuit board as compared to the prior art (FIG. 1A). The presentinvention provides for mechanical protection of fragile bare silicondevices by enclosing these devices inside a light-safe module, leavingno exposed components. The exterior surfaces, therefore, are free of allobstructions which may become damaged during handling or which mayinhibit the placement or display of printed information (e.g.manufacturer's name, logo, date code, part number, patent number, barcode, etc.). Modules free of externally mounted components also simplifythe design of shipping trays and facilitates robotic handling andplacement at the final end-users manufacturing line. Although backwardcompatible with existing SIMM sockets and therefore directly replaceablewith conventional SOJ-type SIMMs, this invention is also capable ofmating with newer sockets that will mount the modules closer together.These newer sockets may mount the modules vertically, horizontally, orin a variety of angles relative to the main circuit board, just aspresent day SIMM sockets. Whichever way the modules are mounted orsocketed, a distinct advantage will be realized for these thin multichipmodules, when the modules are stacked beside one another like sticks ofchewing gum in a package.

Memory devices are the primary semiconductor components supplied onvarious module types today. But, there is also a growing requirement tomodularize other semiconductor components including microprocessors,application specific integrated circuits, telecommunication and otherdevice types. Accordingly, the present invention provides a means forincreasing the number of interconnect pins/pads and improve the thermaldissipation characteristics over present day SIMM module technology.Conceivably, an entire computer can be assembled from specializedfunctions of thin multichip modules, as described herein, into anoverall package approximating the size of a pack of cigarettes.

The molded frame 12 employed in the module of the present inventionoffers yet another improvement over prior art SIMM memory modules whichemploy conventional printed circuit board (PCB) materials. A majority ofSIMM connecting sockets in usage today, require the module thickness tobe tightly controlled across the bottom edge contacts, in order for themodule to function reliably in the socket. Especially if the module isto be frequently inserted and removed from the socket. Standardlamination processes used in the construction of PCB's, result in largethickness variations which are difficult to control. This variation inSIMM thickness directly effects the contact pad pressure exerted againstthe socket contacts, and has been identified as a frequent cause ofintermittent electrical failures. Current practice requires rigorousinspection procedures, adding to the material costs, in order to preventthe inclusion of "out-of-spec" SIMM substrates into the manufacturingline. Substituting a molded frame for this critical component of themodule provides for more consistent dimensional control across thecontact pads and eliminates the necessity for 100% inspection.

An additional benefit gained from a molded frame is the ability to moldcustom features on the module housing that are presently impracticalwith laminate PCBs. Examples of potential molded features includespecial locking mechanisms designed to mate with appropriate structureson the subassembly(s) or mating socket, or finger grips, and keyingmechanisms or other hold fasts.

Methods of Constructing Multichip Modules According to the PresentInvention

A method for constructing a thin multichip module as shown in FIG. 1 aswell as in other embodiments would generally comprise the followingsteps:

assembling a composite substrate;

mounting semiconductor devices on the composite substrate;

testing the semiconductor devices after said step of mounting; and

attaching the composite substrate including said mounted semiconductordevices to a molded frame.

In addition, to the above steps, the method would generally includerepairing any semiconductor devices not operating properly after thestep of testing and prior to attaching the composite substrate to themolded frame.

A method of constructing a thin multichip module such as that shown inFIG. 1 is as follows:

(a) forming a composite semiconductor substrate subassembly including athin laminate circuit and a plurality of semiconductor devices inelectrical contact with the thin laminate circuit, wherein the substratesubassembly includes a plurality of spaced apart contacts;

(b) forming a module frame having a plurality of spaced apart contactsadapted to electrically communicate the contacts on the subassembly; and

(c) attaching the substrate subassembly to the module frame, wherein themodule frame adds rigidity to the substrate subassembly.

As noted, the module frame, and particularly the plurality of spacedapart contacts, are preferably adapted for insertion in a SIMM-typemodule socket. Alternatively, the module can be adapted for insertioninto PCMCIA sockets as desired. As shown in FIG. 1, the module framepreferably includes a floor defining a cavity for receiving thesubstrate subassembly. The step of attaching preferably comprisesattaching the substrate subassembly to the module frame such that thesemiconductor devices are received in the cavity, and wherein theplurality of semiconductor devices are enclosed in the multichip module.In the preferred embodiment, the semiconductor devices are received inthe cavity and preferably do not touch or contact the floor of thecavity. The floor protectively covers the semiconductor devices andprotects the semiconductor devices.

The step of attaching preferably includes attaching the substratesubassembly and module frame in juxtaposition to each other using ananisotropic conductive material between the periphery of the moduleframe and the substrate subassembly.

A second method of forming a thin multichip module comprises the stepsof:

(a) forming a preferably rectangular cover member that is rigid andincludes heat dissipation properties;

(b) forming a generally rectangular thin laminate circuit having aplurality of electrical contacts;

(c) affixing the thin laminate circuit to the inner side of therectangular cover member, preferably by use of an adhesive film;

(d) affixing one or more semiconductor devices to one side of the thinlaminate circuit to form a composite semiconductor substratesubassembly;

(e) forming a modular frame of generally rectangular cross sectionhaving a rectangular cavity to receive the substrate subassembly;

(f) forming a plurality of contacts along at least one edge of themodular frame to make electrical and mechanical contact with theplurality of contacts on the thin laminate circuit of the substratesubassembly;

(g) attaching the substrate subassembly to the module frame so that thecontacts of the subassembly and the frame are electrically connected.

As discussed above, the step of forming the module frame preferablyincludes placing a floor on the lower portion of the module frame. Thesubstrate subassembly is preferably attached to the module frame, andthe floor cooperates with the cover on the substrate subassembly toprotect the semiconductor device from external electrical and mechanicalenvironment. The floor on the module frame is preferably molded as anintegral part of the frame and the cavity is constructed to receive thesemiconductor devices.

Yet another method for forming the thin multichip module of FIG. 1 is asfollows. As discussed above with regard to FIG. 1, the module in FIG. 1includes a composite substrate, a plurality of semiconductor devices, amodule frame to support and protect the semiconductor devices, and meansfor attaching the composite substrate to the modular frame. This methodcomprises the following steps:

(a) forming a generally rectangular module frame having a lower floorforming a cavity adapted for receiving the composite substrate andsemiconductor devices with a plurality of spaced apart contacts along atleast one edge thereof;

(b) forming the composite substrate by attaching a rectangular cover toa thin laminate circuit, preferably using an adhesive film;

(c) attaching the plurality of semiconductor devices to the thinlaminate circuit to form a composite semiconductor substratesubassembly; and

(d) attaching the substrate subassembly into the cavity of the moduleframe, wherein the contacts of the thin laminate circuit are inelectrical communication with the contacts of the module frame.

The step of attaching the substrate subassembly into the cavitypreferably includes applying an anisotropic conductive adhesive ringbounding the cavity of the module frame and contacting the edges of thesubstrate subassembly. The module is preferably designed to be insertedin a standard SIMM socket. However, it is noted that the module may alsobe adapted for insertion into a PCMCIA socket, as desired.

A more comprehensive and detailed method for forming a thin multichipmodule as shown in FIG. 1 is as follows. The module includes thefollowing elements:

(a) a rectangular module frame having a cavity therein and a pluralityof spaced apart contacts along at least one edge;

(b) a composite semiconductor substrate subassembly comprising arectangular coverplate having dimensions similar to the cavity andmodule frame;

(c) a rectangular thin laminate circuit of a rectangular cross section;

(d) an adhesive film for holding the thin laminate circuit adjacent theinner surface of the cover;

(e) a plurality of semiconductor devices of generally rectangularconfiguration attached electrically and mechanically to the side of thethin laminate circuit; and

(f) an anisotropic conductive adhesive ring to connect the substrateassembly interior the cavity of the module frame to provide anencapsulated module with contacts of the frame in electrical cooperationwith the contacts on the thin laminate circuit.

The method for forming the module including the elements listed above isdescribed below:

(1) forming a generally rectangular frame of molded material with alower thin protective cover on its lower edge and a rectangular cavitytherein of a predefined cross section in depth;

(2) forming an isotropic conductive adhesive ring around the parameterof the rectangular cavity and in contact with the module frame;

(3) forming a composite substrate of a rectangular cover having an innersurface, a thin laminate circuit board of general rectangular crosssection affixed to the inner surface of the cover by adhesive film;

(4) forming a composite semiconductor substrate assembly of thecomposite substrate of the thin laminate circuit board, adhesive film,and cover with a plurality of semiconductor devices of generallyrectangular cross section affixed to the lower side of the thin laminatecircuit by means of a direct chip attach, and

(5) forming the completed module by placing the substrate subassemblyinterior of the cavity and affixing the substrate subassembly in themodule frame cavity by the isotropic conductive adhesive ring adjacentthe parameter of the cavity.

A method of forming a composite semiconductor substrate subassembly fora thin multichip module such as that shown in FIG. 4 preferablycomprises the following steps.

(a) forming a rectangular cover plate;

(b) forming a rectangular film adhesive with a plurality of rectangularspaced apart windows therein for cooperation with the cover;

(c) forming a thin laminate circuit of general rectangular configurationhaving a plurality of rectangular spaced apart windows therein and aplurality of contacts along at least one edge thereof;

(d) attaching the thin laminate circuit to the cover plate, preferablyusing the film adhesive; and

(e) mounting a plurality of semiconductor devices, wherein one or moresemiconductor devices are included within each spaced apart window ofthe thin laminate circuit and the adhesive film, wherein a plurality ofleads on the semiconductor devices are placed in electrical contact withthe spaced apart contacts of the thin laminate circuit, and wherein thesemiconductor devices are in direct heat conducting contact with thecover.

As previously mentioned, the film adhesive is positioned between thecover plate and the thin laminate circuit to bond the thin laminatecircuit to the cover plate. Also, the windows in the film adhesive arepreferably aligned with the windows in the thin laminate circuit.

A variation of the above method of forming a composite semiconductorsubstrate subassembly for a thin multichip module is as follows:

(a) forming a rectangular cover plate;

(b) forming a rectangular film adhesive;

(c) forming a thin laminate circuit of general rectangular configurationhaving a plurality of contacts along at least one edge thereof;

(d) attaching the adhesive film to the thin laminate circuit;

(e) forming one or more rectangular spaced apart windows in the laminatecircuit and adhesive film after said step of attaching the adhesive filmto the laminate circuit;

(f) mounting a plurality of semiconductor devices to the cover plate inrespective spaced apart windows of the thin laminate circuit and theadhesive film, wherein a plurality of leads on the semiconductor devicesare placed in electrical contact with the spaced apart contacts of thethin laminate circuit, and wherein the semiconductor devices are indirect heat conducting contact with the cover.

Yet another variation of the above method is as follows. This methodmaximizes the dissipation of heat of the semiconductor devices comprisedin the subassembly. This method comprises:

(a) attaching a thin laminate circuit board with a plurality of spacedapart rectangular apertures therein to a cover for the multichip moduleby adhesive film having a series of rectangular apertures in directregistration of those of the thin laminate circuit; and

(b) attaching a plurality of semiconductor devices to the thin laminatecircuit in registration with the rectangular openings therein wherebythe semiconductor devices are in direct terminal contact with the coveras a heat sink for the semiconductor devices.

A process for forming a dense thin multichip module comprises the stepsof:

(a) forming a generally rectangular frame including a floor definingfirst and second cavities in opposite sides of said floor and aplurality of contacts in spaced apart relation along at least one of theedges thereof;

(b) forming a pair of composite semiconductor substrate assembliescomprising a protective, thermally conductive cover, a thin laminatecircuit affixed to a surface of the cover, and a plurality ofsemiconductor devices attached to the surface of the thin laminatecircuit;

(c) attaching the first substrate subassembly into the first cavity; and

(d) attaching the second substrate subassembly in the second cavity.

In this method, the floor separates the two substrate subassemblies andprovides mechanical rigidity to the multichip module frame. Also, a stepof attaching a flexible circuit to the first and second thin laminatecircuits can be included.

Another method of forming a thin multichip module comprises the stepsof:

forming a generally rectangular flat frame with a floor having an upperand lower surface wherein the floor comprises the interior of the framedefining an upper and lower cavity;

placing first and second laminate circuits on said upper and lowersurfaces of said floor;

placing first and second pluralities of semiconductor devices along theupper and lower surfaces of the floor;

attaching first and second cover members on said upper and lowersurfaces of said frame to protect said first and second pluralities ofsemiconductor devices from external environmental conditions.

A method of forming a thin multichip module such as that shown in FIG.17 is as follows. As previously discussed, the module illustrated inFIG. 17 includes a thin laminate circuit adhesively attached to a coverplate, and a plurality of semiconductor devices electrically andmechanically connected to the thin laminate circuit in operativerelation. This method comprises the steps of:

(a) affixing a thin laminate circuit to a generally rectangular cover;

(b) attaching a plurality of semiconductor devices to the thin laminatecircuit in electrical contact therewith; and

(c) applying a protective coat covering at least a portion of thesemiconductor devices, wherein the protective coat provides rigidity tothe composite semiconductor substrate subassembly.

In this method, the step of applying comprises applying the protectivecoat between the laminate circuit and the semiconductor devices. Thestep of attaching preferably comprises attaching the plurality ofsemiconductor devices to the thin laminate circuit using an anisotropicelectrically conducting adhesive material.

One embodiment of a method for forming a multichip module such as thatshown in FIGS. 18A-B comprises the steps:

forming a cover plate having first and second surfaces;

applying first and second laminate circuits on the first and secondsurfaces of the cover plate; and

applying first and second pluralities of semiconductor devices to saidfirst and second laminate circuits.

A method of forming a thin multichip module such as that shown in FIG.22 comprises the following steps.

(a) forming a generally rectangular thin laminate circuit;

(b) placing one or more electrical contacts into the thin laminatecircuit, said one or more electrical contacts for mating to a connectorframe socket on a circuit board;

(c) affixing the thin laminate circuit to a generally rectangular shapedcover member;

(d) attaching a plurality of semiconductor devices to the thin laminatecircuit; and

(e) folding the thin laminate circuit and cover member along its centerline to provide a U-shaped module wherein one end of the module includessaid one or more electrical contacts and said end is adapted for matingwith the connector frame socket.

In order to construct the module shown in FIG. 24, the thin laminatecircuit is made to include a plurality of windows. The step of attachingpreferably comprises attaching the plurality of semiconductor devicesthrough respective windows in the thin laminate circuit to the covermember.

A second method of forming a thin multichip module as shown in FIG. 22comprising the steps of:

(a) forming a generally rectangular printed circuit board, said printedcircuit board including one or more electrical contacts for mating to aconnector frame socket on a circuit board;

(b) attaching a plurality of semiconductor devices to the printedcircuit board; and

(c) folding the printed circuit board along its center line to provide aU-shaped semiconductor substrate subassembly wherein one end of thesubstrate subassembly is adapted for mating with the connector framesocket.

Yet another method of forming a thin multichip module such as that shownin FIG. 22 comprises the following steps:

(a) forming a generally rectangular thin laminate circuit having firstand second ends, said thin laminate circuit including one or moreelectrical contacts for mating to a connector frame socket on a circuitboard;

(b) affixing the thin laminate circuit to a generally rectangular shapedcover member;

(c) attaching a plurality of semiconductor devices to the thin laminatecircuit; and

(d) folding the thin laminate circuit along its center line to provide aU-shaped wherein one end of the module includes said one or moreelectrical contacts and said end is adapted for mating with theconnector frame socket.

In the above method, the U-shaped module preferably includes a firstfolded end and a second end. The second end is adapted for mating withthe connector frame socket. Also, a protective overcoat can be appliedover the plurality of semiconductor device after said step of attachingsaid plurality of semiconductor devices.

Another process for forming a thin multichip module comprises thefollowing steps:

(a) providing a generally rectangular shaped cover;

(b) folding a rectangular shaped thin laminate board around the coverand affixing to each side of the cover;

(c) attaching a plurality of semiconductor devices to both sides of thelaminate circuit board in mechanical and electrical connectiontherewith; and

(d) placing a protective overlay on the semiconductor devices andlaminate circuit board.

MASS PRODUCTION

Various methods may be used to mass produce the thin multichip modulesof the present invention. Referring now to FIG. 31, a flowchart diagramillustrating a general method for assembling thin multichip modulesaccording to one embodiment of the present invention is shown. In step202 the composite substrate is assembled on a panel as shown in FIG. 32or 33. FIG. 33 illustrates a panel of composite substrates in whichportions of the cover plate has been stamped or excised as representedby the darker shaded area. To facilitate automated handling and volumethroughput, the sub-assembly is preferably assembled as a multiple panelarray. The panel array size is optimized for the capability of theprocessing equipment, and typically ranges from 4×6 inches to 10×15inches. Tooling reference of alignment holes in the comers of the metalcover plate aid in the proper registration of the thin laminatecircuit(s) and adhesive film. The thin metal cover plate in thepreferred embodiment comprises stainless steel sheet stock materialranging in thickness from 0.005-0.010 inches. The metal surface can beplated or treated in a variety of finishes.

As previously discussed, the composite substrate is comprised of a heatdissipating cover plate and a thin laminate circuit applied to the coverplate, preferably using a film adhesive. In step 204 the compositesubstrate is segmented or excised from the panel. In step 206 leads or aflex circuit is attached to the composite substrate edges as required bythe particular design or the particular embodiment. In step 208 theactive semiconductor devices and passive components are connectedmechanically and electrically to the composite substrate. In step 210the substrate subassembly is tested for functionality. In step 212 anprotective epoxy material is overmolded or applied to the underside ofthe mounted devices. In step 214 the subassemblies are segmented fromthe panel array if they have not already been segmented in step 204. Itis noted that in different embodiments it may be desired that thecomposite substrate be separated or segmented from the panel in step 204prior to attaching the semiconductor devices. In other embodiments itmay be more desirable to segment the subassembly from the panel array instep 214 after the semiconductor devices and overcoat have been applied.In step 216 the subassemblies are folded if the respective embodimentrequires the subassemblies to be folded. It is noted that certainembodiments do not require the subassemblies to be folded. In step 218the subassembly is assembled onto the module frame. It is noted that inembodiments similar to that shown in FIG. 1, the subassembly is attachedto the module frame, thereby forming the semiconductor module. In otherembodiments such as those in FIGS. 21 et seq., the subassembly iscompleted without a frame as part of the module and the subassembly isattached to a module socket which in essence acts as the frame of themodule.

Another method comprises the steps of:

forming a cover plate panel, such as that shown in FIG. 30;

forming an array of thin laminate circuits;

affixing the array of thin laminate circuits to the cover plate panel;

removing individual composite substrates from the array of compositesubstrates; and

attaching a plurality of semiconductor devices to each of saidindividual composite substrates.

A method of forming a plurality of composite substrate subassembliescomprising the steps of:

forming an array of thin laminate circuits;

forming a cover plate panel;

punching out portions of said cover plate panel to form an array ofcover plates; and

fixing the array of laminate circuits to the array of cover plates.

Conclusion

Although the method and apparatus of the present invention has beendescribed in connection with the preferred embodiment, it is notintended to be limited to the specific form set forth herein, but on thecontrary, it is intended to cover such alternatives, modifications, andequivalents, as can be reasonably included within the spirit and scopeof the invention as defined by the appended claims.

What is claimed:
 1. A method of forming a thin multichip modulecomprising the steps of:(a) forming a cover member, wherein said covermember is rigid and includes heat dissipation properties; (b) forming athin laminate circuit having a plurality of electrical contacts; (c)affixing said thin laminate circuit to the inner side of the covermember by use of an adhesive film; (d) affixing one or moresemiconductor devices to one side of said thin laminate circuit, to forma composite semiconductor substrate subassembly; (e) forming a moduleframe having a cavity to receive the substrate subassembly; (f) forminga plurality of contacts along at least one edge of the module frame tomake electrical and mechanical contact with the plurality of contacts onthe thin laminate circuit of the substrate subassembly; (g) attachingthe substrate subassembly to the module frame so that the contacts ofthe subassembly and the frame are electrically connected.
 2. The methodof claim 1, wherein said step of forming the module frame includesforming a floor on the lower portion of the module frame;wherein whenthe substrate subassembly is attached to the module frame, the floorcooperates with the cover on the substrate subassembly to protect thesemiconductor device from external electrical and mechanicalenvironment.
 3. A method of forming a thin multichip module inaccordance with claim 1 wherein the floor on the module frame is moldedas an integral part of the frame and the cavity is constructed toreceive the semiconductor devices.
 4. A method of forming a thinmultichip module having a composite substrate, a plurality ofsemiconductor devices, a module frame to support and protect thesemiconductor devices and means for attaching the composite substrate tothe module frame comprising the steps of:(a) forming a module framehaving a lower floor defining a cavity adapted for receiving thecomposite substrate and semiconductor devices with a plurality of spacedapart contacts along at least one edge thereof; (b) forming thecomposite substrate by attaching a cover to a thin laminate circuitusing an adhesive film; (c) attaching the plurality of semiconductordevices to the thin laminate circuit to form a composite semiconductorsubstrate subassembly; and (d) attaching the substrate subassembly intothe cavity of the module frame, wherein the contacts of the thinlaminate circuit are in electrical communication with the contacts ofthe module frame.
 5. The method of claim 4, wherein said step ofattaching the substrate subassembly into the cavity includes applying ananisotropic conductive adhesive ring bounding the cavity of the moduleframe and contacting the edges of the substrate subassembly.
 6. Themethod of claim 4, wherein the module is adapted to be inserted in astandard SIMM socket.
 7. A method of forming a composite semiconductorsubstrate subassembly for a thin multichip module, comprising the stepsof:(a) forming a cover plate; (b) forming a film adhesive with aplurality of spaced apart windows therein for cooperation with thecover; (c) forming a thin laminate circuit having a plurality of spacedapart windows therein and a plurality of contacts along at least oneedge thereof; (d) attaching the thin laminate circuit to the cover plateusing the film adhesive,wherein the film adhesive is positioned betweenthe cover plate and the thin laminate circuit to bond the thin laminatecircuit to the cover plate, and wherein the windows in the film adhesiveare aligned with the windows in the thin laminate circuit, (e) mountinga plurality of semiconductor devices, wherein one or more semiconductordevices are included within each spaced apart window of the thinlaminate circuit and the adhesive film, wherein a plurality of leads onthe semiconductor devices are placed in electrical contact with thespaced apart contacts of the thin laminate circuit, and wherein thesemiconductor devices are in direct heat conducting contact with thecover.
 8. A method of forming a composite semiconductor substratesubassembly for a thin multichip module, comprising the steps of:(a)forming a cover plate; (b) forming a film adhesive; (c) forming a thinlaminate circuit having a plurality of contacts along at least one edgethereof; (d) attaching the adhesive film to the thin laminate circuit;(e) forming one or more spaced apart windows in the laminate circuit andadhesive film after said step of attaching the adhesive film to thelaminate circuit; (f) mounting a plurality of semiconductor devices tothe cover plate in respective spaced apart windows of the thin laminatecircuit and the adhesive film, wherein a plurality of leads on thesemiconductor devices are placed in electrical contact with the spacedapart contacts of the thin laminate circuit, and wherein thesemiconductor devices are in direct heat conducting contact with thecover.
 9. A method of forming a composite semiconductor substratesubassembly for a thin multichip module in order to maximize thedissipation of heat of the semiconductor devices comprised in thesubassembly by the steps of:(a) attaching a thin laminate circuit boardwith a plurality of spaced apart apertures therein to a cover for themultichip module by adhesive film having a series of apertures in directregistration of those of the thin laminate circuit; and (b) attaching aplurality of semiconductor devices to the thin laminate circuit inregistration with the openings therein whereby the semiconductor devicesare in direct thermal contact with the cover as a heat sink for thesemiconductor devices.